The aerosol-based CVD (Chemical Vapor Deposition) method developed at IBEM’s Nanometric Buildings Laboratory (LEDNA) enables the synthesis of aligned carbon nanotubes (VACNTs) in the manner of a carpet-brush, virtually free of by-products and whose length can be controlled over a wide range. LEDNA is able to produce VACNTs on substrates of various kinds and with predetermined characteristics (diameter, length, density). The method developed operates in a single step, with carbonaceous and catalytic precursors injected simultaneously into the reactor. It’s a low-cost process that has been developed right through to industrial production, and has prompted the creation of a start-up company, NawaTechnologies. The aim is to master this process in order to synthesize aligned nanotubes with controlled physico-chemical characteristics for various applications. To achieve this, it is crucial to understand how these nanotubes grow.
The synthesis temperature most often used is around 800°C. Growth can take place directly on the reactor walls or on substrates (quartz, silicon, metals, carbon materials, etc.). For growth on metals or carbonaceous substrates, the deposition of an SiOx barrier underlayer is necessary to avoid carbon accumulation in the substrate (Delmas et al., Nanotechnology 2012). This deposition precedes the feeding of the reactor with the precursors required (ferrocene dissolved in toluene) for CNT growth. Recently, the switch to a gaseous carbon source, namely acetylene, has enabled the synthesis temperature to be lowered to less than 650°C. This change now makes it possible to obtain carbon nanotubes that are thinner (diameter of around 10 nm vs. 20 or 40 nm at higher temperatures, see figure) and denser(1011 vs. 109 CNT/cm² at higher temperatures), and to grow them on low-melting-temperature substrates such as aluminum.
